Gas turbine efficiency generally increases with the temperature of the combustion gas stream. Higher combustion gas stream temperatures, however, may produce higher levels of undesirable emissions such as nitrogen oxides (NOx) and the like. NOx emissions generally are subject to governmental regulations. Improved gas turbine efficiency therefore must be balanced with compliance with emissions regulations.
Lower NOx emission levels may be achieved by providing for good mixing of the fuel stream and the air stream. For example, the fuel stream and the air stream may be premixed in a Dry Low NOx (DLN) combustor before being admitted to a reaction or a combustion zone. Such premixing tends to reduce combustion temperatures and NOx emissions output.
The fuel stream and the air stream are generally premixed in tightly packed bundles of air/fuel premixing tubes to form axial jets in the combustion chamber. The tightly packed bundles of air/fuel premixed axial jets may suffer from blowoff or instability at low-load or part-speed conditions. Accordingly, what is needed is a system that provides reliable, robust ignition and cross-firing, more efficient part-speed and non-loaded operation, and overall improved combustion stability and increased operability when using a DLN combustor having micromixer air/fuel premixing tube bundles.